Detection of the body position while sleeping enables improved unobtrusive monitoring. When an image sensor is used as an off-body motion sensor, motion detection or estimation is typically applied to measure the activity level and replace actigraphs. When e.g. two persons share the bed (65% of the adult US population sleep together with a partner or children) the movements can be easier discerned when the body position is known. Motion detection alone is not sufficient for the shared-bed scenario since the areas of motion cannot indicate sufficiently well which motion areas belong to which subject when the two subjects lie close to each other. Motion estimation, where motion vectors are computed per image block, help, but only in cases when the two subjects do not move similarly in the border area. The body position can indicate which movements are likely to belong to one subject and which movements belong to the other subject.
Moreover, several other benefits regarding the body position information exist, particularly regarding sleep and health. These benefits are                Enable more robust positional apnea detection: Obstructive sleep apnea (OSA) is the most common category of sleep-disordered breathing. In some patients with OSA, the severity of their apnea and sleep disturbance as measured by the Respiratory Disturbance Index (RDI) is twice as high or more when sleeping on their backs (the supine position) compared to sleeping on their sides (the lateral position). This is referred to as Positional Sleep Apnea (“PSA”). By contrast, patients with less or no change in their RDI related to sleeping position are said to have Nonpositional Sleep Apnea (“NSA”). A device designed based on the instant application may help treating patients diagnosed with PSA and increase their and their doctor's insight into the severity and possible progression of their disease. Many people suffering from OSA benefit from sleeping at a 30-degree elevation of the upper body or higher, as if in a recliner. This helps prevent the gravitational collapse of the airway. Lateral positions (sleeping on one's side), as opposed to supine positions (sleeping on the back) are also recommended as a treatment for sleep apnea. Indeed, the gravitational component is smaller in the lateral position than in the supine positions.        Coaching solutions: Body position may be included as a parameter and a user is coached/influenced to bias body positions leading to better sleep quality. The relationship between body position and sleep quality is recognized in the field of sleep research;        Poor sleepers spend longer on their backs with their head straight than good sleepers do;        People who sleep face downwards, on their stomach or on their side, weigh heavily on their jaws with static load, this incorrect position over years can cause symptoms such as migraine, trigeminal neuralgia, pain, hum, tension, and/or dizziness;        Sleep on one's side can ease the symptoms of apnea.        
Complex solutions involving human models and pose recognition exist for detecting the body position of the sleeping person with a camera. They are, however, computationally more complex and only work with a thin blanket where the outline of the person is well visible. Further, such methods do not work for all major body positions (e.g. the distinction between on the stomach and on the back cannot be made).
US20070118054 discloses a method and a system for monitoring vital signs for the prediction and treatment of physiological ailments. In this patent application only the changes in the posture of the body are considered and are estimated from physiological signals. Methods and systems for monitoring vital signs for the prediction and treatment of physiological ailments are provided. The methods and systems disclosed may be applied to the monitoring of a broad range of physiological ailments or “episodes,” including, but not limited to, asthma, hypoglycemia, coughing, edema, sleep apnea, labor, and REM sleep stages. The methods employ sensors, for example, non-contact sensors, adapted to detect vital signs, such as heart rate or respiration rate, to produce signals that can be analyzed for trends, deviations, or for comparison to prior conditions or criteria. The sensors may be positioned whereby the subject need not be viewed by a health care provider. Some methods and systems employ the use of “scores” based upon a combination of sensed vital signs or based upon a comparison of the vital signs to standard criteria.
WO2009/083017 discloses a movement detector for detecting the movement of a breathing activity. To enhance a movement detector for detecting the movement of a body breathing or heartbeat activity comprising a Doppler sensor with a microwave oscillator and at least one mixer in such a manner, that the detector is on the one hand efficient and safe with respect to a baby breathing or heartbeat detection and on the other hand a low cost solution, the sensor is performed as a sensor unit with a volume less than 100 cm and a sending energy lower than 10 mW.
U.S. Pat. No. 5,914,660 discloses a position monitor and alarm apparatus for reducing the possibility of sudden infant death syndrome. A device for reducing the possibility of sudden infant death syndrome (SIDS) as disclosed comprises a position-indicating device effectively coupled to a signal-producing circuit and attached to the clothing of the infant. The position indicating device provides signals, varying in response to prone and other positions assumed by the infant during sleep, allowing an associated alarm device to be activated in response to the infant's assuming a SIDS-dangerous prone or side-position. In one embodiment, the position of the infant can be determined by an optical sensor interacting with a reflective or other marker adhered to the infant. Gravity or pressure switches may also be used to provide position-responsive signals. A signal generated upon assumption of the SIDS-dangerous prone or side-positions is transmitted to a remote receiver located proximate the infant's care-giver whereupon an alarm is generated to indicate the need to reposition the infant. A constant low-level or intermitted maintenance signal can be produced to assure the continued and proper operation of the apparatus. An additional awakening alarm can be produced near the sleeping infant to further reduce the likelihood of a SIDS event.
US2010/0262026 discloses a method for the detection of the sleep position. The method as disclosed in US2010/0262026 uses ECG sensors at fixed positions, not fixed to the patient. The ECG signals recorded from the sensors are used to detect body position, using the variation of ECG potential over the surface of the body. The results may be processed by measuring artifacts related to the angle between the sensors and the heart, in particular the polarity of the QRS complex. The sensors may be fixed on the upper surface of a bed and used to monitor the sleep position.